The school was never placed on lockdown because the incident was over very quickly, said HISD Assistant Police Chief Robert Mock.

"No students were ever in any danger," Mock said.

Mock said police spotted a suspicious vehicle, described as a lime green truck, in the student parking lot.

He said an officer saw the truck pull into a space next to a black pickup truck. When the officer went to investigate, he saw one suspect inside the black pickup and ordered the person out of the vehicle.

The person then got into the green truck. The driver drove toward the officer, who fired one shot.

It's unclear if either of the suspects was wounded or if the pickup was hit.

The driver of the green pickup is described as Hispanic, in his early to mid-20s. He was about 6 feet tall and weighed about 250 pounds. No description of the other suspect was available.

School principal Ross McAlpine said once the shooting was reported, he notified district officials and sent out a telephone call to parents informing them of the incident.

It took about 45 minutes to get the notification out to parents.

McAlpine said the students were not at risk of harm as a result of the incident and that students and staff went about their normal daily routine.

The HISD officer will be on administrative duty until the investigation is complete, which is standard procedure when an officer fires his weapon.

A few parents who showed up at the campus said they had not been contacted by district officials about the shooting. They were concerned for their children and came to the school after they had heard about incident on social media or their children had called them.

Jacqueline Williams said her 17-year-old son called her and told her about the gunfire. She said he told her he heard shots fired and that he was hiding in a campus bathroom. He pleaded with her to come to the school to pick him up before anybody tried to hurt him. After they hung up, she said she called him back but his phone didn't answer.

When she got to the school, she was told that nobody had been hurt. She didn't see her son, but she was satisfied that he was safe.